OBJECTIVES: A. To study the EcoB restriction DNase/ATPase and modification methylase to 1. understand how it can be broken nonspecifically, yet receive only a defined number of breaks; 2. understand the role of each subunit of the enzyme in the reaction; 3. determine the structure of the 3'- and 5'-terminal formed by the DNase, and of the recognition site of the enzymes; 4. understand the significance of the EcoB restriction ATPase; 5. understand the relationship to and interactions with other host and virus metabolic functions. B. To study the reaction of the recBC DNase/ATPase by electron microscopy to learn about its role in DNA recombination. To study the ATPase-mediated melting reaction biochemically, and to study the phage T7 inhibitor of the enzyme. C. To study the specificity and significance of some new endonucleases (now called E. coli endonucleases III and V).